The present invention relates generally to thin film integrated component devices, and more specifically to an improved fabrication process that involves fabricating both anodized metal capacitors and high temperature deposition (HTD) capacitors within the same device with a minimum number of mask operations.
Given the trend of the miniaturization of electronics for devices such as cell phones and personal digital assistants (PDAs), the use of thin film integrated component devices is increasing. Active and passive components can be integrated on a thin film substrate material such as glass or ceramic. Integrated capacitors can be formed on the substrate in several ways. Examples of methods are the anodized metal method and the HTD method.
The anodized metal method of fabricating a capacitor on a thin film substrate consists of depositing a layer of conductive metal (e.g., aluminum, tantalum, or other anodizable metal) on the thin film substrate, coating the metal layer with a photoresist layer, and forming a metal oxide layer (i.e., the capacitor""s dielectric layer) from the metal layer. After the metal oxide layer is formed, the photoresist layer is stripped. The conductive metal layer and the metal oxide layer are then cleaned using an etching process and a final conductive metal layer is deposited to form the integrated capacitor.
The high temperature deposition method of fabricating a capacitor on a thin film substrate consists of depositing a conductive metal layer (e.g., aluminum) on the thin film substrate, followed by the deposition at high temperature of a dielectric layer (e.g., silicon nitride). A photoresist layer is deposited and the dielectric layer is then etched. A final conductive layer is deposited to form the integrated capacitor.
These two types of capacitors have distinctive properties, which are preferable depending upon the application. An anodized metal capacitor is preferable when a large capacitance is required. Because it is composed of high capacitance density material the desired capacitance can be realized with a capacitor of manageable size. Similarly, if a small capacitance is desired, using a high density capacitor would mean the size of the capacitor would have to be extremely small. In small capacitance applications, using a high temperature deposition capacitor (e.g., silicon nitride capacitor) is preferable.
For some applications it may be desirable to have both types of capacitor as part of the same integrated circuit. The integration of the devices is problematic in that the fabrication process of one device may cause defects in another device on the same substrate.
For example, if the anodized metal capacitor is fabricated first, then the etching process of the high temperature deposition capacitor may destroy the anodized metal layer of the capacitor. If the high temperature deposition capacitor is fabricated first, then the aluminum layer may experience hillocking. Hillocking may occur due to the deposition of the thin film dielectric which is done at temperatures above that at which the aluminum layer is deposited. This may cause the aluminum to recrystalize to relieve stress in the film. The recrystalization causes small hillocks (bumps) on the metal""s surface. These defects can cause the film to break when a potential is applied. Anodization is difficult to do successfully on aluminum with hillocks. The anodized layer on aluminum with hillocks is more likely to break down at lower voltages. Also, the hillocks can sometimes become sufficiently large so as to grind through the insulating levels and short-circuit a component.
An integrated passive component device is described comprising a first capacitor of a first of a first type and a second capacitor of a second type. A protective conductive metal layer is disposed between the dielectric layer of the first capacitor and the dielectric layer of the second capacitor. The protective conductive metal layer helps to prevent process chemicals and conditions, used to fabricate the dielectric layer of the second capacitor, from adversely affecting the dielectric layer of the second capacitor. The two types of capacitors are fabricated on the same substrate using only one masking operation.
An improved method for fabricating anodized capacitors and high temperature capacitors on the same device is also described. The improvement comprises depositing a protective conductive metal layer as the top conducting plate of the anodized capacitor. The protective conductive metal layer protects the anodized metal layer of the anodized metal capacitor from the etching process of the high temperature deposition capacitor.
Other features and advantages of the present invention will be apparent from the accompanying drawings and from the detailed description that follows below.